Permanent magnet



Patented Sept. 26, 1933 UNITED STATES 1,928,382 PERMANENT MAGNET Werner Kiister, Dortmund, Germany, assignor to Vereinigte Stahlwerke Aktiengesellschaft,

Dusseldorf, Germany No Drawing. Application May 12, 1931, Serial No. 536,950, and in Germany May 23, 1930 3 Claims; (01. 175-21) This invention relatesto permanent magnets resistant to changes of temperature.

The magnets hitherto manufactured by hardening a relatively high carbon steel are not resistant 5 to temperature changes or annealing. The martensitic structure which they exhibit and which is the cause of their magnetic values gradually changes even at lower temperatures. At the same time the magnetic hardness constantly de- 0 creases. If therefore such a magnet be built into an apparatus which operates at elevated temperatures then on cooling to lower temperatures, for example, room temperature, the said magnet does not revert to its original state.

The present invention obviates the foregoing drawback and relates to a permanent magnet which is resistant to temperature changesdue to its manufacture from a' special kind of ferromagnetic alloy which is adapted to be agehardened, that is to say, which can be improved by a precipitation hardening and which is after such precipitation hardening stable against the high temperatures to which it had been subjected during the annealing treatment causing the precipitation hardening. These alloys are first quenched for the purpose of attaining their highest magnetic properties, and then annealed at elevated temperatures (up to about 700 C.). In consequence of this heat treatment they are 9 completely stable to temperature changes up to the previous annealing temperature. After heating to elevated temperatures they revert to their initial values on cooling. This property is frequently very desirable in the construction of machines, apparatus and measuring instruments.

It could however, up to the present, not be attained with the magnetic alloys hitherto usual. Such requirements are for example, made in the construction of temperature regulators, contacts, measuring instruments and the like.

By Way of example an alloy may be mentioned, the main constituents of which are 15 per cent of tungsten and 30 per cent of cobalt, the remainder being iron. If such an alloy be quenched from 1200 C. and be annealed for one hour at 700 C. there is thus obtained a coercive force of about 85 gausses. The alloy thus treated can now be heated, to a temperature of about 700 C. without its magnetic hardness being decreased thereby. This process is generally known as age hardening" or precipitation hardening.

I claim:

1. A permanent magnet resistant to temperature changes which comprises a ferromagnetic alloy magnetically stable against temperature changes up to about 700 C.

2. A permanent magnet resistant to temperature changes which comprises a ferromagnetic alloy subjected to precipitation hardening, containing as main constituents, 15 per cent of tungsten and 30 per cent of cobalt and the remainder iron.

3. A method of preparing an alloy for permanent magnets, which consists in precipitation hardening of a ferromagnetic alloy by first quenching said alloy from a temperature of about 1200 C. for the purpose of obtaining its highest magnetic properties, and then annealing the alloy at temperatures up to 700 C., said alloy containing as main constituents approximately 15% tungsten, 30 cobalt and the remainder iron.

WERNER KSTER.

DISCLAIMER 1,928,382.-Wemer Kdster, Dortmund, Germany. PERMANENT MAGNET. Patent dated September 26, 1933.

Deutsche Edelstahlwerke A. G. Hereboy V Disclaimer filed August 2, 1938, by the assignee,

enters this disclaimer to" claim 1 in said specification. fiic'ial Gazette September 6, 1938.] 

